This invention relates to sheet feeding, and more particularly to the feeding of sheets of corrugated cardboard and the like from a stack to a downstream apparatus such as a conveyor.
It has long been known to place a stack of sheets on a vertically movable platform and feed the sheets off the top of the stack one at a time in succession while raising the platform. Various feeding devices have been utilized in connection with this concept.
One of the most difficult problems in sheet feeding is that of sheet warpage. If the sheets in the stack are warped and the feeding device receives a warped sheet from the top of the stack, the sheet may jam in the apparatus. This is especially true at high speeds, such as 1000 ft./min.
It is a task of the present invention to provide a concept wherein, broadly, sheet material which is either flat or warped may be efficiently and quickly fed from the top of a stack with little or no opportunity for jamming and the resultant possible damage to the sheet material and/or the feeding apparatus.
It is a further task of the invention to provide a way to feed such sheet material through a narrow slot without said jamming.
It is yet another task of the invention to automatically control the stack lifting operation so that there is cooperation with the sheet material feeding operation.
In accordance with one aspect of the invention, a floating feed device is adapted to be engaged by the top sheet in the rising stack and to feed the sheet downstream. The mount for the feed device is articulated, and the device includes a vacuum chamber and horizontal drive rollers.
In accordance with another aspect of the invention, a narrow slot is formed between a guide roller of the feed device and a gate which is disposed in the plane of a stack back-up plate and which is vertically movable in said plane. A control is provided to maintain the same slot width, no matter what the articulated position of said guide roller, by automatically adjusting the gate vertically with the guide roller.
In accordance with a further aspect of the invention, the feed device is caused to articulate about its mount upon engagement by a rising stack, and such articulation causes a resultant change in the speed of the stack lift drive.